In recent years, conversion of an electrical signal into an optical signal has been attempted, corresponding to a requirement for high-speed signal transmission in a module, and interface BGAs that interconvert electricity and light have been developed. The interface BGAs can perform optical connection as well as electric connection. FIG. 32 illustrates a fundamental structure of an interface BGA. As shown in FIG. 32, the interface BGA includes a semiconductor device 81, a packaging substrate 82, and solder balls 83. In order to transmit and receive high-speed signals, the packaging substrate 82 includes surface emitting lasers 84 for transmitting signals and photodiodes (not shown) for receiving signals on the bottom face side. The surface emitting lasers 84 and the photodiodes are sealed with a resin layer 86. Furthermore, microlenses 85 are arranged on the resin layer 86.
FIG. 33 shows a mode of mounting the interface BGA on a printed circuit board. The semiconductor device 81 and the packaging substrate 82 are mounted on a printed circuit board 97 via the solder balls 83. Since the solder balls 83 are used for the mounting, the distance W between the packaging substrate 82 and the printed circuit board 97 is equal to the diameter of the solder balls 83 and is usually 400 μm. Light emitted from the surface emitting laser 84 is collimated by the microlens 85 so that crosstalk between the adjacent optical signals is not caused when the light is scattered in this distance W. The optical signals, when reached a microlens 95 on the printed circuit board 97 side, are collected by a microlens 95 and then guided to an optical waveguide 98 (Non-Patent Document 1).
In order to guide the optical signals collected by the microlens 95 to the optical waveguide 98, for example, a mirror 99 inclining by 45° is disposed in the optical waveguide 98 to change the optical path by 90°. In another method, an end face of the core of an optical fiber as the optical waveguide 98 is diced by an inclination of 45°, and the cut surface is deposited with, for example, Ag or Al (Non-Patent Documents 2 and 3). These are the same in the case that optical signals transmitted along a plane of the printed circuit board 97 in the optical waveguide 98 are sent up by 90° to be transmitted to the semiconductor device 81.
The microlens can be produced by, for example, a resist reflow method. In this method, a resin layer formed on a substrate is patterned into a cylindrical shape by a photolithographic method and then reflowed by heating, so that a microlens is formed by surface tension of the resin.    [Non-Patent Document 1] NIKKEI ELECTRONICS, Dec. 3, 2001, p. 124.    [Non-Patent Document 2] M. Kinoshita, et al., “Thin film formation for photonic device by epitaxial lift-off (ELO) technique, MES2003, The 13th Micro-Electronics Symposium, October, 2003, pp. 380-383.    [Non-Patent Document 3] T. Ishitsuka, et al. “Experimental production of optical module with printed board, MES2003, The 13th Micro-Electronics Symposium, October, 2003, pp. 388-391.